1. Field of the Invention
This invention relates to electric motors, specifically to an electric motor where the rotor of the motor also functions as a drive wheel.
2. Description of the Related Art
At least three United States patents apply to electric motors where a portion of the electric motor serves as a drive wheel, rather than providing power to a shaft which transfers such power to another component. These are U.S. Pat. No. 3,548,965 of John J. Pierro; U.S. Pat. No. 5,164,623 of Vasily V. Shkondin; and U.S. Pat. No. 5,721,473 of LeRoy M. DeVries.
U.S. Pat. No. 3,548,965 involves a rather complicated rotor primarily composed of two adjacent ferromagnetic circles, each having projections which extend toward the other circle and which projections from one circle are interdigitated with the projections from another circle. The rotor, itself, contains no magnetxe2x80x94either permanent or electromagnetic. A field excitation coil projects a magnetic field into both circles of the rotor. (It is stated that in some cases the field excitation coil may be replaced with one or more permanent magnets.) The magnetic field created by the field excitation coil interacts with a magnetic field created by stator conductor windings. To produce rotation of the rotor, the electric current through the stator conductor windings is supplied at a frequency which is calculated from a formula which includes the tangential velocity of the rotor. Such tangential velocity is determined by a commutator which is xe2x80x9cpreferably of electromagnetic type . . . xe2x80x9d
The motor of U.S. Pat. No. 5,164,623 utilizes a mechanic commutator, whichxe2x80x94being a mechanical device in which different physical parts make moving contact with one anotherxe2x80x94is subject to wear as well as physical breakage and, therefore, to malfunction. Additionally, from the drawings it appears that the electromagnets of the rotor are located radially outward from the (preferably permanent) magnets of the stator. The disclosure and claims merely state that the xe2x80x9cmagnetic membersxe2x80x9d of the stator are mounted on the circumference of the stator and face the electromagnets of the rotor.
And the rotor associated with the motor of U.S. Pat. No. 5,721,473 includes both permanent magnets and electromagnets. It is suggested on lines 62 through 64 in column 5 of U.S. Pat. No. 5,721,473 that the electromagnets of the rotor are necessary in order to achieve adequate acceleration: xe2x80x9cWhen the electromagnets 16 are magnetized and incited by the wire coil stator 17, a wheel accelerates very fast.xe2x80x9d And, although the disclosure does not clearly specify the orientation of the magnets on the rotor with respect to the xe2x80x9cwire coil stator,xe2x80x9d the drawings and the claim indicate that the magnets of the rotor are located radially outward from the xe2x80x9cwire coil stator.xe2x80x9d In pertinent part, the claim states: xe2x80x9ca tire and rim rotor which includes a plurality of oppositely placed interchangeable permanent and electro magnets that rotate said tire and rim rotor by means of an electric field excited by an interchangeable wire coil stator secured onto a stationary axle . . . xe2x80x9d
In its description of the prior art, U.S. Pat. No. 5,164,623 discusses several patents issued by the former Soviet Union but states that the xe2x80x9cindependent-drive wheel[s]xe2x80x9d of such patents have xe2x80x9cpoor controllability because of the absence of a link between dynamics of rotation and control signals.xe2x80x9d
The present Electric Motor with Rotor Being a Drive Wheel minimizes the possibility of failure by not utilizing mechanical commutators. Moreover, the current invention does not require the use of a formula to compute a frequency for the time when the electromagnets should be energized.
In the present invention, permanent magnets are placed upon one or both of the lateral sides of the drive wheel, forming the rotor. Electromagnets are attached to the structure that supports the axle for the drive wheel, creating the stator. Such electromagnets are arranged generally in a plane that is substantially parallel to, but not within, the plane or planes containing the permanent magnets and are sufficiently close to the permanent magnets that the magnetic fields of the electromagnets and the permanent magnets will interact with one another. If permanent magnets are placed upon both of the lateral sides of the drive wheel, electromagnets may be placed upon both sides of the structure that supports the axle for the drive wheel.
A sensor mounted on the structure that supports the axle for the drive wheel simply determines when a pole of a permanent magnet approaches or is near such sensor. The sensor is so located (1) that when such pole approaches or is near the sensor, magnetic attraction or repulsion between the permanent magnet and an electromagnet will produce a force in the direction that it is desired to rotate the drive wheel and (2) that when the opposite pole of the electromagnet approaches or is near the sensor, magnetic attraction or repulsion between the permanent magnet and an electromagnet would not produce a force in the direction that it is desired to rotate the drive wheel.
Three methods are employed for utilizing the information from the sensor both (1) to assure that the electromagnets will be energized only when such energization will produce a force in the desired direction and (2) to control the speed of the drive wheel.
The control of speed depends upon the fact that the speed of the drive wheel is proportional to the average power (and, therefore, the average voltage) supplied to the electromagnets. Consequently, the speed of the drive wheel is determined by regulating the average voltage that is supplied to the electromagnets.
All three methods control such average voltage by regulating the percentage of time that voltage is supplied to the electromagnets. This is accomplished by closing a switch (preferably an electronic switchxe2x80x94such as a transistor, a triac, or a semiconductor-controlled rectifier), i.e., substantially reducing the resistance between the terminals of the switch, in a circuit between a source of electrical energy, preferably a battery or other generator of direct current, and the electromagnets for such desired percentage of time.
To assure that force is produced only in the desired direction, the first method for closing the switch operates only between the time that the first pole of a permanent magnet approaches the sensor and the time that the second pole of the permanent magnet approaches the sensor; the second and third methods, only when a pole of polarity to which the sensor is sensitive is near such sensor. Outside of such periods, the switch is left open because no signal is sent to close such switch.
In the first method, input of the desired speed can be provided to a computer through any means that is well known in the art. The sensor is in communication with the computer and informs the computer when a pole of a permanent magnet has approached the sensor. The computer then begins producing a signal to close the switch. Preferably, the output signal from the computer will be in the form of a square wave, i.e., a periodic wave which has a constant voltage amplitude when the output is being supplied and zero amplitude during the remainder of the period. The computer communicates with the switch so that the output signal from the computer is sent to the switch and causes such switch to be closed for the proportion of the period during which the output from the computer is non-zero, i.e. when a voltage is being supplied by the computer. The computer adjusts the non-zero proportion of the period to achieve the desired average voltage being transmitted from the source of electrical energy through the switch to the electromagnets and, consequently, the desired average speed of the drive wheel. When the sensor detects that the opposite pole of the permanent magnet has approached the sensor, the sensor so informs the computer; and the computer terminates the production of an output signal, causing the switch to be open.
In a second method, the computer is replaced with a timing circuit which establishes one specific proportion of the period during which such timing circuit produces an output voltage of constant amplitude and which produces no output voltage for the remainder of the period. This proportion can only be changed by adjusting the value of an electric component, such as a potentiometer, within the timing circuit.
When the second method is employed, the sensor, which is preferably a Hall-effect switch, will produce a current or voltage that is utilized, in any manner that is well known in the artxe2x80x94such as by completing an electrical circuit from a source of electrical energy, to cause the timing circuit to begin and to continue operating only while a pole of a given polarity is near the sensor. Therefore, when a pole of a permanent magnet to which the sensor is sensitive is near the sensor, the sensor will initiate and maintain the operation of the timing circuit, which in turn will periodically close a switch, preferably an electronic switch, to energize the electromagnets. Such switch will remain closed only so long as it receives a voltage output from the timing circuit. When the opposite pole of the permanent magnet (or no pole) is near the sensor, the sensor will produce no current; the timing circuit will not be activated; and the switch will, consequently, not remain closed.
Alternatively, with the second method, two sensors could be located near each other. One sensor could be sensitive to one magnetic pole; the other sensor, to the other magnetic pole. (This can be accomplished by, for example, reversing the Hall-effect switch.) Then the average power and, consequently, the speed of the drive wheel would be increased.
Additionally, one sensor may be utilized to activate all the electromagnets; or there can be separate sensors for one or more electromagnets.
In a third method, the sensor acts just as in the second method. The sensor, however, communicates directly with the switch so that the voltage from the sensor is transmitted directly to the switch and acts just as does the output voltage from the timing circuit. Therefore, with the third method, no mechanism is included to alter the average voltage that is produced by the source of electrical power. The voltage produced by the source of electrical power is sent continuously to the electromagnets throughout the time that a pole of a permanent magnet to which the sensor is sensitive is near the sensor.
When the third method is used, the options with respect to sensors that were discussed for the second method are again available; and it is preferred to have a separate sensor for each electromagnet.
With all three methods the electrical signal from the sensor is either on or off (not a continuum of possible values). Therefore, with the first method, the computer can be programmed to invert the signal it sends to the switch. (Alternatively, and inverter could be placedxe2x80x94preferably through electronic switching operated by a userxe2x80x94between the sensor and the computer.) This will cause the switch controlling current to the electromagnets to be activated at the times other than those when magnetic attraction or repulsion between the permanent magnet and an electromagnet will produce a force in the original direction that it was desired to rotate the drive wheel. This will, consequently, at times produce no force and at other times produce a force that tends to cause the drive wheel to rotate in the reverse direction. If the drive wheel were already rotating in a forward direction, this would initially have a braking effect. If continued, it would ultimately result in the drive wheel rotating in the reverse direction. Of course, it would be more efficient to employ a sensor that is so located (1) that when a specific type of pole approaches or is near the sensor, magnetic attraction or repulsion between the permanent magnet and an electromagnet will produce a force to rotate the drive wheel in the reverse direction and (2) that when the opposite pole of the electromagnet approaches or is near the sensor, magnetic attraction or repulsion between the permanent magnet and an electromagnet would not produce a force to rotate the drive wheel in the reverse direction. And this more efficient technique is within the scope of the present invention.
Similarly, to obtain a force that tends to rotate the drive wheel in a reverse direction with the second method, an inverter is placed (preferably through electronic switching operated by a user) between the sensor and the timing circuit. And to accomplish this feat with the third method, an inverter is placed (preferably through electronic switching operated by a user) between the sensor and the switch.
Alternatively with any of the three methods, one or more additional switches or an H-bridge may be employed to enable current to flow through the electromagnets in a reverse direction. This would, of course, tend to cause the drive wheel to rotate in the reverse direction. If the drive wheel were already rotating in a forward direction, this would initially have a braking effect. If continued, it would ultimately result in the drive wheel rotating in the reverse direction.
In the case of the first method, the computer can send signals directing the additional switch or switches to be set so that the current would flow through the electromagnets in a forward direction or signals directing the switches to be set so that the current would flow through the electromagnets in a reverse direction. For the second and third methods, some outside force (electronic or manual) would have to activate the additional switch or switches.
The computer also has the ability to protect the motor by delaying activation of the electromagnets until the wheel has attained a desired operational speed through the application of an outside force, i.e., a force that does not result from the present invention. And the computer can be programmed to utilize the signal from the sensor to determine the speed of rotation of the drive wheel.
Furthermore, when it is desired to have more than one drive wheel operating with one another, a single computer can perform the desired computer functions for all the drive wheels.
Although the source of electrical power for the motor is preferably direct current, the motor will function with alternating current provided that the a. c. voltage is biased so that it never has a negative value. Furthermore, any method that is well known in the art can be used to control the average voltage that is supplied to the electromagnets, although the first two methods described above are preferred, with the first method being more preferred.
The ends of the core of each electromagnet are preferably bent toward the permanent magnets in order to increase the attractive and repulsive forces.
Moreover, it has been experimentally determined that the cores of the electromagnets perform more effectively when such cores are composed, ignoring the bent portion at the ends, of identical sections that are laminated with the plane of lamination being substantially parallel to the plane in which the electromagnet lies. Also, it has been experimentally determined that the electromagnets perform more effectively when they are wound with multi-strand wire.
Preferably, the structure that supports the axle for the drive wheel contains a cavity that communicates with the electromagnets and can contain either a heat-transfer medium or a heat-absorbing medium to reduce heat near the electromagnets. When a heat-transfer medium is to be employed, the cavity also communicates with at least one radiating surface, such radiating surface preferably being either composed of carbon-filled nylon plastic or a metal fin.
Optionally, the electromagnets are encapsulated within a module having at least one radiating surface, such radiating surface preferably being either metal fins or fins composed of a carbon-filled nylon plastic. The module is removably inserted into the structure that supports the axle for the drive wheel. Within a cavity of the module is placed a heat-transfer medium (a fluid or gel) which communicates with both the electromagnets and the radiating surface, thereby conducting heat from the electromagnets to the radiating surface, from which such heat is transferred to the surrounding environment.
Moreover, in a still further alternative, the electromagnets can either simply be air cooled or may have liquid circulated between such electromagnets and a radiating heat sink through tubes or passages. When the tubes are utilized, a unique magnetic pump is employed that is operated by a magnetic connection between the rotating permanent magnets and a permanent magnet located in the impeller of the pump. And air cooling may be aided by the attachment of a fan to the structure that supports the axle for the drive wheel.
The simultaneous alignment of more than one electromagnet with more than one permanent magnet, which is termed xe2x80x9ccogging,xe2x80x9d increases drag. Any technique which will prevent such cogging, such as having the spacing between electromagnets different from that between permanent magnets or having the distance between poles of electromagnets different from that between poles of adjacent permanent magnets, is, therefore preferred.
Also, to prevent energy losses caused by coupling between electromagnets, pairs of electromagnets are preferably activated alternately by the computer in the first method; by placing a flip-flop between the output of the timing circuit and the electromagnets in the second method; and, if a single sensor, is utilized for all electromagnets, placing a flip-flop between the sensor and the electromagnets in the third method.